Bone anchor assemblies can be used in orthopedic surgery to fix bone during healing, fusion, or other processes. In spinal surgery, for example, bone anchor assemblies can be used to secure a spinal fixation element to one or more vertebrae to rigidly or dynamically stabilize the spine.
Bone anchor assemblies can also be used as an engagement point for manipulating bone (e.g., distracting, compressing, or rotating one vertebra with respect to another vertebra, reducing fractures in a long bone, and so forth). In these instances, a distractor or other instrument can be used to apply a manipulation force to the bone anchor assembly and, by extension, to the bone in which the bone anchor assembly is implanted.
Traditional bone anchor distraction systems typically rely on gripping the outer portion of a polyaxial receiver member of the bone anchor assembly. This can be undesirable in some instances, as there is a potential for interference to occur in situations where adjacent receiver members abut against one another (especially at L5-S1) resulting in an inability to properly place the distraction instrument over the receiver member. In addition, distraction systems that rely on gripping the outer portion of the receiver member cannot achieve true parallel distraction unless rods and set screws are also placed within the receiver member to lock off its polyaxial degree of freedom. The requirement that rods and set screws be in place in order to achieve true parallel distraction can be cumbersome for surgeons who prefer to distract off of the bone anchor assemblies to maximize visualization in preparation for any discectomy and interbody work (e.g., PLIF or TLIF procedures). Other distraction systems attempt to achieve true parallel distraction in the absence of rods and set screws by directly engaging with the shank of the bone anchor assembly. This can also be undesirable, however, as the extensions of the distraction instrument can mechanically interfere with one another, especially in regions of the lumbar spine with high lordosis (e.g., L5-S1), making distraction very difficult to perform.
Another shortcoming of existing distraction systems is that they generally can only be attached to a bone anchor assembly after it has been inserted into the bone. Feeding a distraction tool over a receiver member of a bone anchor assembly after it has already been inserted into the bone can be difficult and time-consuming for the surgeon.
There is a continual need for improved systems and related methods for manipulating bone.